*{
  padding: 0;
  margin: 0;
}
.container{
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  width: 100vw;
  height: 100vh;
  background: black;
}
.container a{
  display: block;
  width: 100px;
  height: 40px;
  color:aqua;
  text-align: center;
  line-height: 40px;
  font-size: 16px;
  text-decoration: none;
  margin: 40px;
  position: relative;
  transition: all 0.3s ease-in-out;
  /* 滤镜 var()函数 */
  filter: hue-rotate(calc(var(--i) * 60deg));
}
.container a::before,.container a::after{
  content: "";
  position: absolute;
  width: 20px;
  height: 20px;
  border:2px solid aqua;
  transition:all 0.3s ease-in-out 0.3s;
}
.container a::before{
  top:0px;
  left: 0px;
  border-bottom: 0px;
  border-right: 0px;
}
.container a::after{
  bottom: 0px;
  right: 0px;
  border-left: 0px;
  border-top: 0px;
}
.container a:hover{
  background-color: aqua;
  box-shadow: 0px 0px 30px aqua;
  color:black;
  -webkit-box-reflect: below 1px linear-gradient(transparent,rgba(0,0,0,.3));
  transition-delay: 0.3s;
}
.container a:hover::before,.container a:hover::after{
  width:98px ;
  height: 38px;
  transition-delay: 0s;
}